In the conventional plastic optical fibers comprising a core of polymethylmethacrylate (PMPA), polycarbonate or like polymer, vinylidene fluoridetetrafluoroethylene copolymer (Japanese Examined Patent Publication No.21600/1978), fluoroalkylmethacrylate copolymer (Japanese Examined Patent Publication No. 8978/1968) and the like are usually used as a cladding.
The vinylidene fluoride-tetrafluoroethylene copolymers having good adherence to PMMA as the core and high flexibility, however, have the drawbacks of being low in working temperature of up to about 70.degree. C. and relatively high in transmission loss of about 200 dB/km due to the crystalline structure of the polymers.
The fluoroalkylmethacrylate copolymers are low in transmission loss due to high transparency of the polymers and have improved working temperature of about 85.degree. C. However, the fluoroalkylmethacylate copolymers have the drawback of being low in adherence to the PMMA core which results in the poor flexibility of the optical fibers.